What materials are in vapor retarders?

What materials are in vapor retarders?

Prevalent vapor barrier materials used over the years have been polyethylene (Type 1), asphalt-impregnated or asphalt-coated kraft paper (Type 2) and foil skrim kraft (FSK) (Type 1) – paper-backed aluminum.

What is a Class 2 vapor retarder?

Class II vapor retarders have a permeance level between 0.1 perm and 1 perm and are considered semi-impermeable. Examples include unfaced expanded polystyrene, fiber faced polyisocyanurate and asphalt-backed kraft paper facing on fiber glass batt insulation.

What are the different types of Vapor retarders?

Sheet polyethylene (visqueen) or unperforated aluminum foil (FSK) are Class I vapor retarders. Class II – Low permeability vapor retarders – rated greater than 0.1 perms and less than or equal to 1.0 perms. The kraft facing on batts qualify as a Class II vapor retarder.

What is the International Building Code for vapor retarder?

At that time (2004) the International Building Code (and its derivative codes) defined a vapor retarder as 1.0 perm or less, equivalent to Lstiburek’s definition of a Class II vapor retarder. In the paper, Lstiburek provided examples of 14 different wall assemblies designed with the minimum vapor retarders proposed.

What should Perm rating be for vapor retarder?

Any material that has a perm rating of 1 or less is considered to be an adequate vapor retarder for residential construction. (A perm rating is a measure of the diffusion of water vapor through a material.)

Is a Class 1 vapor retarder good enough for crawl space?

Essentially, this section of code is saying that if you cover the walls and ground of your crawl space with a Class I vapor retarder (known as encapsulating) you can remove or close off your ventilation to the exterior. For more information on the pros and cons of ventilation, you can read my blog article about eliminating crawl space vents .